The acetylcholine receptor on skeletal muscle is subject to changes in functional properties during development. We have shown that this altered function results from the expression of an acetylcholine receptor channel type bearing faster gating kinetics. This proposal examines two aspects of this change in gating. First, what is the role of nerve in causing increased expression of the fast gated channel type? To this end, we will test the idea that nerve causes endplate specific changes in gating through neuronal "imprinting", by denervation of embryonic muscle just prior to the onset of developmental changes in channel gating. Also, we will directly evaluate neuronal effects on gating by study of embryonic muscle co-cultured with neurons or neuron-conditioned medium. Finally, the hypothesis that endplate specific channel gating exists will be tested by direct comparison of junctional and non-junctional channel gating on mature muscle. The second major question addressed by this proposal relates to the metabolic requirements for changes in channel function. Is the appearance of the fast gated channel type the result of a newly synthesized channel type or the result of altered functional properties of the pre-existing "embryonic" slow gated channel type? For this purpose, we will take advantage of the fact that the developmental change in receptor kinetics, observed in vivo, continues to occur on tissue-cultured embryonic muscle. Both single channel and noise analysis techniques will be used to quantitate the developmental alterations in channel function in vitro. These experiments form the basis for understanding the molecular mechanisms underlying the long term changes in acetylcholine receptor channel function.